Researchers from the Yunnan Observatories have investigated the relationships between the tilt angles of sunspot groups during the declining phase and the parameters of the next solar cycle. The related research result, "Relationship between the Tilt Angles of Sunspot Groups and the Properties of the Next Solar Cycle", has been recently published in the Astrophysical Journal.

The tilt angle of the sunspot group is a crucial parameter in the conversion of the toroidal magnetic field to the poloidal magnetic field, which is at the heart of the Babcock–Leighton-type dynamo model. Solar physicists generally believe that a larger tilt angle contributes more significantly to the poloidal field, which serves as the source of the toroidal field responsible for solar activity during the next solar cycle. 

However, this study revealed that there is no statistically significant correlation between the mean tilt angle during the declining phase and the strength or amplitude of the next solar cycle. The correlation between the mean tilt angle and the tilt-angle scatter during the declining phase was also found to be statistically insignificant. 

Furthermore, the researchers found a significant anti-correlation between the variability of the tilt angles during the declining phase and both the strength and amplitude of the next solar cycle. These findings indicate that the modulation of the parameters of the next solar cycle by the tilt-angle scatter during the declining phase plays a vital role in regulating solar-cycle variability. Additionally, the study found that the tilt-angle scatter shows significant anti-correlations with the mean area of the sunspot groups, the total area of the sunspot groups, and the percentage of large sunspot groups. 

These results suggest that weaker solar activity during the declining phase is indicative of weaker solar activity during the subsequent solar cycle, and conversely, stronger activity during the declining phase is predictive of stronger activity in the next cycle.

Figure 1, the standard deviation of the tilt angles during the declining phase vs. the strength, and amplitude of the next solar cycle. Image by GAO.

Contact:
GAO Pengxin
Yunnan Observatories, CAS
E-mail:gaopengxin@ynao.ac.cn